A conventional type of breathing protective apparatus is one wherein breathing gas, usually compressed air, is supplied through a hose to a demand valve connected with the mask of the user. During inhalation, the user receives the required amount of air and then exhaled gas is discharged to the surrounding atmosphere. The breathing mask may be maintained at slightly higher than ambient pressure, preventing inward leakage of toxic contaminants. However, in a confined environment where a high level of hydrocarbon gases or vapours are present, exhaled gas containing unused oxygen may create a potential explosion hazard.
Problems with the above described type of breathing apparatus are also evident if it must be used in an oxygen free inerted atmosphere, as discharge of oxygen into an inerted environment will require an additional costly inerting operation.
In order to increase efficiency in some closed-circuit under water breathing apparatus, the diver's exhaust gas is pumped back to a bell or submersible unit for CO.sub.2 removal, reconstitution and recirculation. Due to the complexity of such a system, weight and high costs, that type of apparatus cannot be utilized as a breathing protective means for working in a contaminated atmosphere.
In more complex decompression chambers, a special oxygen breathing mask is employed to eliminate a need for a high ventilation rate for oxygen removal during oxygen breathing. This type of mask has a common demand valve controlling the oxygen flow during an inhalation, and an exhalation valve connected through a hose and dumping means with an outside decompression chamber. The small exhaust capacity of the exhalation valve when used with a vacuum source, and lack of positive pressure in the mask to prevent leaks of toxic contaminants, eliminates the possibility of using it for moderate work in atmospheres containing toxic gases or vapours.
The present invention overcomes the above mentioned problems by providing an improved breathing protective apparatus with an inhalation regulator and primary source of breathing air supplied to the user through a pressure line, and an exhalation regulator with a return line connected to a vacuum source to remove exhaust gases from the work area, the apparatus having a positive pressure and free flowing regulator to provide an extra measure of safety in a toxic environment and to provide low breathing resistance under high work load conditions.
Another feature of the invention is to provide a breathing apparatus of the type described, wherein a failure of the supply-return lines will allow a user to switch to an emergency air supply and bypass the exhaust regulator.
Yet another feature is to provide a breathing apparatus wherein bypassing the exhalation regulator for exhaust without vacuum conditions will automatically eliminate positive pressure and free flowing regulator to save emergency air for escape from a contaminated environment.
According to a broad aspect, the present invention relates to a breathing protective apparatus including a facemask having a regulator housing incorporating an inlet valve, an inhalation diaphragm controlling said inlet valve, an exhalation diaphragm and an outlet valve controlled thereby, a supply line connecting said inlet valve with a source of breathable air pumped under pressure to said valve; a return line connecting said outlet valve with a source of vacuum; said outlet valve and diaphragm therefor being so arranged that movement towards a closed position exerts a force on inlet valve lever means to create a positive pressure and small free flow in the facemask and regulator housing.